This invention relates to nonwoven web composites of improved cohecency which exhibit a combination of excellent durability, absorbency, and/or other desirable properties. More specifically, the invention is directed to nonwoven web composites containing a bicomponent filament matrix having adhesive properties, and a third component selected from fibers and particles contained within the matrix.
Bicomponent nonwoven filaments are known in the art generally as thermoplastic filaments which employ at least two different polymers combined together in a heterogeneous fashion. Instead of being homogeneously blended, two polymers may, for instance, be combined in a side-by-side configuration, so that a first side of a filament is composed of a first polymer xe2x80x9cAxe2x80x9d and a second side of the filament is composed of a second polymer xe2x80x9cB.xe2x80x9d Alternatively, the polymers may be combined in a sheath-core configuration, so that an outer sheath layer of a filament is composed of a first polymer xe2x80x9cA,xe2x80x9d and the inner core is composed of a second polymer xe2x80x9cB.xe2x80x9d Alternatively, the polymers may be combined in an islands-in-the-sea configuration in which one or more islands of a first polymer xe2x80x9cAxe2x80x9d appear in a sea of a second polymer xe2x80x9cB.xe2x80x9d Other heterogeneous configurations are also possible.
Bicomponent filaments offer a combination of desired properties. For instance, certain polypropylene resins yield filaments which are strong but not particularly soft. Certain polyethylene resins yield filaments which are soft but not particularly strong. By combining both resins together in the form of bicomponent nonwoven filaments, a hybrid combination of strength and softness can be achieved.
Bicomponent filaments have been disclosed in combination with carbon particles, zeolites, ion exchange resins, carbon filters, sterilizing fibers, and/or gas adsorbing fibers for use in specialized filters. U.S. Pat. No. 5,670,044, issued to Ogata et al., discloses the use of bicomponent meltblown filaments in these combinations, for use in cylindrical filters. In that case, the bicomponent filaments contain high and low melting polymers. The filaments of the filter are stacked and bonded together by melting only the lower melting component.
Pulp fibers have been employed in certain absorbent applications to enhance the absorbency. U.S. Pat. No. 4,530,353, issued to Lauritzen, discloses pulp fibers in combination with staple length bicomponent fibers used in the manufacture of absorbent bandages. In that case, the fibers also contain high and low melting polymers. The staple length fibers are bonded together by melting only the lower melting component.
In applications where a third component selected from fibers and/or particles is combined with a bicomponent filament web, the bicomponent filaments act as a matrix which ensnares, entraps, and contains the third component. In some of these applications (for instance, absorbent applications where the third component is an absorbent), there is a need or desire to increase the amount of the third component in order to maximize the properties that it contributes to the nonwoven web composite. There is also a need or desire to improve the containment properties of the bicomponent filament matrix at all levels of third component loading.
The present invention is directed to an improved nonwoven web composite including a matrix of bicomponent thermoplastic filaments and a third component selected from fibers, particles, and combinations thereof contained within the filaments. The nonwoven web composite exhibits improved containment of the third component, permitting higher loading of the third component as well as improved durability at all loading levels. The present invention is also directed to an absorbent article, including a personal care absorbent article, which utilizes the improved nonwoven web composite of the invention.
The bicomponent thermoplastic filaments contain at least first and second thermoplastic polymer components, arranged in distinct segments or zones across the width of the filament. At least one of the thermoplastic polymers possesses adhesive properties with respect to the third component, or is modified to possess adhesive properties with respect to the third component. The adhesive properties may be imparted by either a) employing an adhesive polymer for at least one of the distinct thermoplastic polymer segments in the bicomponent filaments, which segment is exposed at the filament surface, b) modifying a non-adhesive polymer by blending it with an adhesive polymer and employing the blend for one of the distinct polymer segments in the bicomponent filaments, which segment is exposed at the filament surface, or c) surface-modifying the bicomponent filaments or a segment thereof by spraying, dipping, or otherwise applying an adhesive material effective to bond the bicomponent filaments to the third component.
With the foregoing in mind, it is a feature and advantage of the invention to provide a nonwoven web composite containing a filament matrix and a loaded component (fibers and/or particles) within the matrix, having improved durability and stability due to adhesion between the filament matrix and loaded component.
It is also a feature and advantage of the invention to provide an absorbent nonwoven web composite capable of containing high loadings of absorbent fibers and/or particles, due to adhesion between the absorbent material and the nonwoven thermoplastic filament matrix which contains it.
It is also a feature and advantage of the invention to provide an absorbent article having improved absorption and durability, due to better continence of absorbent fibers and/or particles within a nonwoven filament matrix, and a higher loading capacity for the absorbent fibers and/or particles.
The term xe2x80x9cnonwoven fabric or webxe2x80x9d means a web having a structure of individual fibers or threads which are interlaid, but not in a regular or identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as, for example, meltblowing processes, spunbonding processes, air laying processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91.)
The term xe2x80x9cmicrofibersxe2x80x9d means small diameter fibers having an average diameter not greater than about 75 microns, for example, having an average diameter of from about 1 micron to about 50 microns, or more particularly, having an average diameter of from about 1 micron to about 30 microns. Another frequently used expression of fiber diameter is denier, which is defined as grams per 9000 meters of a fiber. For a fiber having circular cross-section, denier may be calculated as fiber diameter in microns squared, multiplied by the density in grams/cc, multiplied by 0.00707. A lower denier indicates a finer fiber and a higher denier indicates a thicker or heavier fiber. For example, the diameter of a polypropylene fiber given as 15 microns may be converted to denier by squaring, multiplying the result by 0.89 g/cc and multiplying by 0.00707. Thus, a 15 micron polypropylene fiber has a denier of about 1.42 (152xc3x970.89xc3x970.00707=1.415). Outside the United States the unit of measurement is more commonly the xe2x80x9ctex,xe2x80x9d which is defined as the grams per kilometer of fiber. Tex may be calculated as denier/9.
The term xe2x80x9cspunbonded fibersxe2x80x9d refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinnerette having a circular or other configuration, with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of which is incorporated herein in its entirety by reference. Spunbond fibers are quenched and deposited onto a collecting surface. Spunbond fibers are generally continuous and often have average diameters larger than about 7 microns, more particularly, between about 10 and 30 microns.
The term xe2x80x9cmeltblown fibersxe2x80x9d means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 to Butin. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in diameter, and are generally self bonding when deposited onto a collecting surface. Meltblown fibers used in the present invention are preferably substantially continuous in length.
The term xe2x80x9csubstantially continuous filaments of fibersxe2x80x9d refers to filaments or fibers prepared by extrusion from a spinnerette, including without limitation spunbonded and meltblown fibers, which are not cut from their original length prior to being formed into a nonwoven web or fabric. Substantially continuous filaments or fibers may have average lengths ranging from greater than about 15 cm to more than one meter, and up to the length of the nonwoven web or fabric being formed. The definition of xe2x80x9csubstantially continuous filaments or fibersxe2x80x9d includes those which are not cut prior to being formed into a nonwoven web or fabric, but which are later cut when the nonwoven web or fabric is cut.
The term xe2x80x9cstaple fibersxe2x80x9d means fibers which are natural or cut from a manufactured filament prior to forming into a web, and which have an average length ranging from about 0.1-15 cm, more commonly about 0.2-7 cm.
The term xe2x80x9cpulp fibersxe2x80x9d refers to fibers from natural sources such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for instance, cotton, flax, esparto grass, milkweed, straw, jute hemp, and bagasse.
The term xe2x80x9caverage pulp fiber lengthxe2x80x9d refers to a weighted average length of pulp determined using a Kajaani fiber analyzer Model No. FS-100 available from Kajaani Oy Electronics in Kajaani, Finland. Under the test procedure, a fiber sample is treated with a macerating liquid to ensure that no fiber bundles or shives are present. Each fiber sample is dispersed in hot water and diluted to about a 0.001% concentration. Individual test samples are drawn in approximately 50 to 500 ml portions from the dilute solution and tested using the standard Kajaani fiber analysis procedure. The weighted average fiber lengths may be expressed by the following equation:       ∑                  X        i             greater than       0        k    ⁢            (                        X          i                *                  n          i                    )        /    n  
where
k=maximum fiber length,
Xi=individual fiber length,
ni=number of fibers having length Xi 
and
n=total number of fibers measured.
The term xe2x80x9csuperabsorbent materialxe2x80x9d refers to a water-swellable, water-insoluble organic or inorganic material capable, under the most favorable conditions, of absorbing at least 20 times its weight, preferably at least about 30 times its weight in an aqueous solution containing 0.9% by weight sodium chloride.
The term xe2x80x9cpolymerxe2x80x9d generally includes without limitation homopolymers, copolymers (including, for example, block, graft, random and alternating copolymers), terpolymers, etc., and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term xe2x80x9cpolymerxe2x80x9d shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic and atactic symmetries.
The term xe2x80x9cbicomponent filaments or fibersxe2x80x9d refers to fibers which have been formed from at least two polymers extruded from separate extruders but spun together to form one fiber. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the bicomponent fibers and extend continuously along the length of the bicomponent fibers. The configuration of such a bicomponent fiber may be, for example, a sheath/core arrangement wherein one polymer is surrounded by another, or may be a side-by-side arrangement or an xe2x80x9cislands-in-the-seaxe2x80x9d arrangement. Bicomponent fibers are taught in U.S. Pat. No. 5,108,820 to Kaneko et al., U.S. Pat. No. 5,336,552 to Strack et al., and U.S. Pat. No. 5,382,400 to Pike et al., each of which is incorporated herein in its entirety by reference. For two component fibers, the polymers may be present in ratios of 75/25, 50/50, 25/75 or any other desired ratios. Conventional additives, such as pigments and surfactants, may be incorporated into one or more polymer streams, or applied to the filament surfaces.
The terms xe2x80x9cadhesive polymer,xe2x80x9d xe2x80x9cadhesive polymer blendxe2x80x9d and xe2x80x9cadhesive filamentxe2x80x9d refer to any polymer, polymer blend or filament containing them which exhibit a sticking force to a third component fiber or particle, no matter how small. This includes any kind of adhesion or tack. If a fiber or particle exhibits a binding force to, or reluctance to separate from, a thermoplastic polymer filament when the filament is positioned adjacent the fiber or particle and the fiber or particle is subject to a gravitational or other pulling or sliding force, then at least one polymer in the filament exhibits a sticking (i.e., adhesive) force to the fiber or particle.
The terms xe2x80x9cadhesive-modified polymer,xe2x80x9d xe2x80x9cadhesive modified polymer blendxe2x80x9d and xe2x80x9cadhesive-modified filamentxe2x80x9d refer to a polymer, polymer blend, or filament containing them which has been modified (through surface coating, blending, or otherwise) so that it exhibits an adhesive force to a fiber or particle, as defined above.
The term xe2x80x9cbicomponent filaments having adhesive propertiesxe2x80x9d refers to any adhesive bicomponent filament as well as to any adhesive-modified bicomponent filament.
The term xe2x80x9cpersonal care absorbent articlexe2x80x9d includes diapers, training pants, swim wear, absorbent underpants, baby wipes, adult incontinence products and feminine hygiene products.
The term xe2x80x9cthrough-air bondingxe2x80x9d or xe2x80x9cTABxe2x80x9d means a process of bonding a nonwoven, for example, a bicomponent fiber web in which air which is sufficiently hot to melt one of the polymers of which the fibers of the web are made is forced through the web. The air velocity is often between 100 and 500 feet per minute and the dwell time may be as long as 6 seconds. The melting and resolidification of the polymer provides the bonding. Through-air bonding has restricted variability and is generally regarded as a second step bonding process. Since TAB requires the melting of at least one component to accomplish bonding, it is restricted to webs with two components such as bicomponent fiber webs or webs containing an adhesive fiber or powder.
The term xe2x80x9cthermal point bondingxe2x80x9d involves passing a fabric or web of fibers to be bonded between a heated calender roll and an anvil roll. The calender roll is usually, though not always, patterned in some way so that the entire fabric is not bonded across its entire surface. As a result, various patterns for calender rolls have been developed for functional as well as aesthetic reasons. One example of a pattern has points and is the Hansen Pennings or xe2x80x9cHandPxe2x80x9d pattern with about a 30% bond area with about 200 bonds/square inch as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings. The HandP pattern has square point or pin bonding areas wherein each pin has a side dimension of 0.038 inches (0.965 mm), a spacing of 0.070 inches (1.778 mm) between pins, and a depth of bonding of 0.023 inches (0.584 mm). The resulting pattern has a bonded area of about 29.5%. Another typical point bonding pattern is the expanded Hansen and Pennings or xe2x80x9cEHPxe2x80x9d bond pattern which produces a 15% bond area with a square pin having a side dimension of 0.037 inches (0.94 mm), a pin spacing of 0.097 inches (2.464 mm) and a depth of 0.039 inches (0.991 mm). Another typical point bonding pattern designated xe2x80x9c714xe2x80x9d has square pin bonding areas wherein each pin has a side dimension of 0.023 inches, a spacing of 0.062 inches (1.575 mm) between pins, and a depth of bonding of 0.033 inches (0.838 mm). The resulting pattern has a bonded area of about 15%. Yet another common pattern is the C-Star pattern which has a bond area of about 16.9%. The C-Star pattern has a cross-directional bar or xe2x80x9ccorduroyxe2x80x9d design interrupted by shooting stars. Other common patterns include a diamond pattern with repeating and slightly offset diamonds and a wire weave pattern looking as the name suggests, e.g., like a window screen. Typically, the percent bonding area varies from around 10% to around 30% of the area of the fabric laminate web. As is well known in the art, the spot bonding holds the laminate layers together as well as imparts integrity to each individual layer by bonding filaments and/or fibers within each layer.